1. Field of the Invention
The present invention relates to: a firing furnace that is used for manufacturing a honeycomb structural body made of ceramics, a ceramic material and the like; a porous ceramic member manufacturing method using the same; and a porous ceramic member manufactured by the manufacturing method.
2. Discussion of the Background
There have been proposed various exhaust gas purifying honeycomb filters and catalyst supporting members which are used for purifying exhaust gases discharged from internal combustion engines of vehicles such as a bus, a truck and the like, construction machines and the like.
With respect to the exhaust gas purifying honeycomb filters and the like, there has been used a honeycomb structural body which is constituted by a non-oxide based ceramic porous body such as silicon carbide and has a superior heat resistance.
Conventionally, for example, JP-A 2001-48657 and JP-A 63-302291 have disclosed firing furnaces used for manufacturing non-oxide based ceramic members of this type.
The firing furnace to be used for manufacturing such non-oxide ceramic members is provided with a heater and the like in the furnace and a heat insulating layer mainly made of carbon.
In the case where a porous ceramic member made of silicon carbide is manufactured by using the above-mentioned firing furnace, since a formed body after a degreasing process is heated and fired at a high temperature of 1400° C. or more, gases including silicon carbide, silicon, SiO gases and the like are discharged into an ambient atmosphere inside the firing furnace, and these gases react with carbon members inside the firing furnace to be converted into silicon carbide and the like.
When the carbon members are converted into silicon carbide, there arises a difference in physical property such as thermal expansion coefficient between a surface layer of the heat insulating layer made of silicon carbide and an inner layer made of carbon. Thus, warping tends to occur in the heat insulating layer. Moreover, in combination with the conversion into silicon carbide and the like, reaction of carbon with oxygen remaining inside the furnace or with oxygen and the like generated from the formed body causes corrosion in the heat insulating layer.
When warping and corrosion occur in the heat insulating layer, the heat insulating performance is lowered, or separation or the like occurs in the heat insulating layer, making the firing furnace unable to function as a furnace; consequently, the heat insulating layer needs to be exchanged. However, changing the heat insulating layer requires high costs, resulting in a problem of high manufacturing costs.
Moreover, even if the heat insulating layer does not need to be changed, an efficient heating process is no longer available and firing costs increase when the heat insulating property of the firing furnace is deteriorated.
The contents of Japanese Patent Laid-Open Publication No. 2001-48657 and Japanese Patent Laid-Open Publication No. 1988-302291 are incorporated herein by reference in their entirety.